System of current-wave transmission



May 8, 1923. 1,454,495-

H. J. VENNES SYSTEM OF CURRENT WAVE TRANSMISSION Filed May 26 1919 NET Patented May 8, 1923.

UNITED STATES HABALD J. VENNES, OF NEW YORK, N. Y., ASSIGNOR TO WESTERN ELECTRIC COMPANY,

PATENT OFFICE.

INCORPORATED, OF NEW YORK, N. Y., A CORPORATION OF NEW YORK.

SYSTEM OF CURRENT-WAVE TRANSMISSION.

Application flied May 26,

To all whom it may concern:

Be it known that I, HARALD J. VnNNEs, a citizen of the United States, residing at New York, in the county of New York, State of New York, have invented certain new and useful Improvements in Systems of (Jurrent-W'ave Transmission, of which the following is a full, clear, concise, and exact description.

This invention relates to two-way selective transmission of currents, and particularly to the two-way transmission of modulated currents.

More specifically the invention relates to the prevention of interference between outgoing and incoming transmissions where a current of a given frequency is modulated for transmission in both directions. By the provisions of the invention, selectivity between outgoing and incoming transmissions is obtained even for modulations of the same base-frequency current.

It has been shown that when a high frequency current is modulated by a band of low frequency currents the resultant current may be resolved into a current of the original high frequency and two side bands of frequencies respectively less than and more than the original high frequency. A high frequency carrier wave, when modulated in accordance with speech, for example, possesses these characteristics. It is also known that in order to reproduce the low frequency modulating currents, for example, to receive the speech from the speech modulated current, it is not necessary that both side hands he received, but it is sufficient if one side band is present. It is customary in modulated wave transmission to suppress at the transmitter one of the side bands and the original high frequency wave and to transmit only the remaining side band of frequencies, again supplying the necessary high frequency current at the receiving point from a local source. Heretofore, it has been the practice to transmit in both directions the corresponding side band of the same high frequency, for example, the side band of frequencies less than the original high frequency. For a given low frequency modulating wave, therefore, transmitted over the same high frequency channel in both directions, there will be current of the same frequency fed into the channel and, at the same time, received from the channel at the same 1919. Serial No. 299,748.

station, and this requires a precise balancing of the transmitter and receiver with respect to the channel, and imposes obectionable limitations upon the relative amounts of energy that are being fed into and derived from the channel. According to the invention one side band of frequencies, ,for example, the resultant band of frequencies less than the original high frequency is transmitted in one direction, and the opposite side hand, in this case of frequencies higher than the original high frequency, is transmitted in the opposite direction, so that at a given station, the transmitted and the received frequencies derived from modulated current of the same high frequency are quite different and the requirement for an exact balance and the objectionable limitations mentioned are obviated.

In the drawing terminal circuits for a system according to the invention are diagrammatically shown for two-way transmission between a high frequency carrier current line HF and each low frequency line LF, and LF,.

Each line has a net circuit for balancing for the transmitted frequencies and has the usual conjugate arrangement for transmitting to and from the respective lines. Currents received over the low frequency line LF, are impressed through couplings 1 and 2 upon the input of the modulator M,. Current of carrier frequencv f, is continuously supplied to the input side of the modulator M from the source 3, which is connected to the terminals of the potentiometer 4. Normally, the effects of this current of frequency f, on the two parallel paths of the modulator are equal and neutraiize each other in the common output coil 5, so that when no currents are impressed through the coupling 2 upon the modulator, there is no resultant transmission of current of frequency f, through the modulator. The currents received from line LF,, however, cause the potential of the grids 6 and 7 at any instant to be varied oppositely and the impedance of one of the discharge devices 8 or 9 to be increased. while the impedance of the other discharge device is decreased, so that current from source 3 produces a net resultant current-flow through coil 5 as long as the received current from line LF, persists. If the frequency or the band of frequencies of the modulating current is indicated by s, the current in the output coil 5 is a substantially pure modulated current resolvable into frequencies f 8 and f +s. The band filter 10. to which output coil 5 is coupled by means of coil 11. is so proportioned that it transmits freely the currents composing the band f +s, but prevents frequencies outside this range from reaching the leads 12. 13. The currents of frequency f.|s. however. are transmitted through leads 12 and 13 and coils 14 to the high frequency line HF.

At another similar station on line l'll lhcre may be a similar source of current of frequency f a source of modulating current of requency s. a modulator similar to M and a filter which will transmit to the line HF only the currents of frequency f s. Currents of these frequencies received at the station indicated in the drawing form overline HF pass through the leads 15 and 16 and through the band filter 20. which is so proportioned as to pass currents of the band of frequencies f,s', but to prevent the transmission of currents outside this frequency range... These incoming currents are fed through the coupling 21 to the input of the detector 1),. The current component of frequency f., which is necessary for the detection of the modulating components comprised in the received currents. is supplied fromsource 3 which is connected across the potentiometer 22. The action of detector D is the converse of that described of modulator llL. that is, it acts to produce in its out ut coils 23 the low frequency currents w iich were conveyed over the line HF as modulations of the high frequency f.. These detected low frequency currents pass through the filter 24 freely and are supplied over line LF but any high frequency currents that may have reached the coils 23 are not transmitted by filter 24.

If, as has been the practice heretofore. the filters 10 and .20 were designed to pass the same frequencies. 11-8, for example. and if this band of frequencies were transmitted in both directions over line HF, any unbalance of the line circuit relative to the circuits including leads 12. 13 and leads 15, 16 would cause part of the relatively large transmitting currents from the leads 12. 13 to feed back into the input of the detector D By the system of the invention, however. in the event of some unbalance of the line HF as to the transmitting and receiv ing circuits. currents from the modulator M. and filter 10 are of such frequency as not to be passed by filter 20 back to detector D The system of the invention is thus seen to possess the advantages of the staggered carrier frequency system. in which carrier frequencies used for transmitting in one direction are intermediate those used for the other direction but the invention makes possible a smaller frequency interval between transmissions. The principle utilized in the invention may be termed staggering of the signaling currents.

u an entirely similar manner, two-way communication between the low frequency line LF and the-main line HF ma be had. In this case a source 25 of carrier requency J is provided for so plying the modulator M and the detector IR, which may be similar respectively to M and D and the band filters 26 and 27 are designed to transmit re spectively the frequencies f +8 and f s, the .9 representing the low frequency or band affine" frequency currents. carried by line Separate sources 3 and 25 of high frequency currents have been indicated to simplify the drawing. but in practice it would be usual to derive the different carrier frequencies as harmonics of the output wave of a generator of suitable type located either at the station shown or at a distant point on the line HF.

Only two different two-way channels on the multiplex line. HF are provided for in the circuit illustrated, but it is obvious that other channels may be furnished by supplying other high frequency carrier currents and transmitting and receiving circuits. The filters for transmitting. to the line HF would be connected to the leads 1? and 13, for instance, similarly to filters 10 and 26. and filters for received currents from the line Ill would be connected to leads 1:) and 16.

In place of the lines LF and LF the transmitters and the receivers assumed to be in circuit on said lines might equally well be connected directly to the modulators and detectors, respectively.

While the invention has been described with reference to speech transmission by way of example. it is equally applicable to other kinds of signal transmission. and in fact to selective transmission in general. Also the invention is not to be limited to transmission of currents or waves on wires, but it is evident that an antenna might replace the high frequency line terminal illustrated. and the invention be used for radio transmission.

\Vhile the invention has been illustrated and described with reference to a particular circuit. arrangement. it is to be understood that it is not to be limited either to the specific arrangement as a whole or to the particular details. but only by the scope of the appended claims.

\Vhat is claimed is:

1. The method of two-way transmission of electric energy which comprises mod: lating at, each of a pair of communicating stations a given high frequency wave in accordance with signals and deriving at the respective stations from the wave so modulated, wave components of a given character for transmission in one direction, and wave components of a different character for transmission in the opposite direction.

2. In twoway transmission of signals by means of a carrier current of a givenfrequeue modulated in accordance with said sigma the method which comprises deriving from the modulated current at the respective communicating stations current components of a given-character for transmission in one direction and current components of a difien cnt character for transmission in the opposite direction.

3. The method of selective signaling which comprises translating signals into modulations of a sustained high frequency current at each of a pair of communicating stations so that the high frequency current contains components of higher and of lower frequenoies and transmitting only said higher requency components for sign in one direction, and transmitting only said lower frequency components for signaling in another direction.

4. The method of twoway current transmission which comprises producing at each of two locations at current of a given frequency, varying each said current so that it has components of a higher frequency and components of a lower frequency than said given frequency, and transmitting between said locations in one direction the components of the higher frequencies and in the other direction the components of the lower frequencies than said given frequency.

5. The method of twoway transmission of high frequency current modulated by a. band of low frequency currents which comprises transmitting from a. station in one direction one side band of the resultant frequencies and transmitting to the station in the opposite direction the other side band of the resultant frequencies.

6. In the transmimion of high frequency current modulated by low frequency currents, whereby resultant current of the hi h frequency and two side bands of frequencies are obtained, the method which comprises suppressing the high frequency component of the modulated wave, transmitting one side band of fr uencies in one direction between two communicating stations and transmitting the other side band of frequencies in the oppositc direction between the said stations.

7. In a system of two-way transmission of modulated waves of a given base frequency, the method of securing increased selectivity between transmissions to and from a given station which comprises transmitting from said station wave components of a given character derived from modulating current of said base frequency, and receiving from said system at said station current components of a diferent character derived from current of said base frequency.

8. In a transmission system, stations, sources of current of the some freque at the respective stations, means coopera g with said sources for producing currents having ranges of frequencies, and means for transmitting a range of said fr uencies between said stations in one direction and for transmitting another range of said frequencies in the opposite direction between said stations.

9. In a transmission system, means for modulatinfrwaves of agiven high frequeuc at a plura ty of stations in accordance wit a plurality of low frequencies, means at one of said stations for selectively transmitting a portion of the resulting waves and receiving a different portion; and means at another of said stations for selectively receiving and transmitting portions corresponding respectively thereto.

10. In a transmission system, a line, means for transmittin on said line currents comprising one .si band of frequencies of a modulated high frequency current, and means for transmitting in the opposite direction on said line currents comprising the alternate side band of frequencies of a modulated current of the same high frequency.

11. In a transmission system, a line having stations thereon, means at the several stations for producing modulated current of the same base frequency, means at each station for transmitting selectively a portion of said modulated current of different frequency characteristic from that transmitted by another said station.

12. In 'a multiplex transmission system, a

line havin a plurality of two-way communication c annels each defined b a frequency ran obtained by modulating a single base requency, means for confining transmission in one. direction through each said channel to a rtion of said frequency range, and means or confining transmission in the opposite direction to a different portion of said frequency range.

13. A transmission line, a source of alternoting current, a modulator and a. detector supplied with current from said source, a source of modulating energy for said modulator, a. band filter for associatin said modulator with said line, and a ban filter of different fr uency characteristic for associating said etector with said line. 0

14-. A line having stations thereon, means at each station for producing current of the same base frequency and for modifyin said current by currents of other frequencies, a receiver at each station, circuits for supplying current of given character from said means at a first station through said line to said receiver at a second station. and circuits for supplying current of different frequency characteristic from said means at said second station through said lineto said receiver at said first station.

15. In a multiplex signaling system, a line with stations thereon, each station having means for producing high frequency current for said line, and means for detectin said current, and means for modulating sai current in accordance with signals so as to produce a pure modulated wave comprising the sum frequencies of a high freiquency plus signal fre uencies and the di erence frequencies 0 high frequency minus signal frequencies; a filter at one said station for transmitting from said modulating means to said line only the sum frequencies, a filter at the same station for transmitting from said line to said detectin means only the difierence frequencies, the detecting means and modulating means at another said station being arranged to cooperate with said filters and with both said means at said one station.

16. The method of twoway transmission of signalsbetween a pair of communicating stations comprising modulating carrier current of a single frequency in accordance with said signals and staggering the components of the modulated wave for transmission in the two directions.

17. In the two-way transmission of signals used to modulate at the respective communicating stations a carrier current of a single frequency the method which comprises normally suppressing the current of carrier frequency and staggering the components of the modulated wave.

18. A telephone system comprising means for producing voice-modulated currents of the same base frequency at two stations, means for selectively transmitting a range of the resulting frequencies in one direction between said stations and means for selectively transmitting a different range of the resulting frequencies in the opposite direction between said stations.

19. A telephone system including stations,

transmitting means at each station for producing voice modulated current of the same base frequency, and means at each station for receiving voice modulated current of said base frequency, a pair of filters at each of the respectivestations, one of each pair selective to current of a given frequency characteristic for transmission, and the other selective to current of a different frequency characteristic for reception, the filters at each station having the same frequency characteristics as those at the other station but related to the transmitting and receiving means at the same station'in an inverse frequency order as compared with the other station.

In witness whereof, I hereunto subscribe my name this 15th day of May, A. D. 1919.

HARALD- J. VENNES. 

